Crude Oil and Fractional Spillages Resulting from Exploration and Exploitation in Niger-Delta Region of Nigeria: A Review About the Environmental and Public Health Impact

The Niger Delta basin of Nigeria situates on the continental margin of the Gulf of Guinea in the equatorial West Africa between latitudes 3o and 6o North and longitudes 5o and 8o East. The word “Delta” is derived from a Greek alphabet in shape of a pyramidal triangle. A delta is a geographical feature formed when a River diversifies into numerous streams that sometimes inter-connect into an intricate web of Rivers, lagoons, swamps and wet land. The point where the main rivers divides is the top of the pyramid while the base is where the division ends or the River enters the sea or larger water course such as a lake. The Niger Delta on the Atlantic coast is one of the moist important in the world. Other worlds notable Deltas include the Nile, Mississippi, Orinoco, Ganges and Mekong (Ibru, 2001). Deltas are usually fertile, contain diverse resources and are therefore noted for large human settlements and civilizations. The Niger Delta complex is one of the most prominent basins in West Africa and actually the largest delta in Africa. It includes the Imo River and Cross River deltas and extends into the continental margins of Cameroun and Equatorial Guinea (Reijers et al 1996).


Introduction
The Niger Delta basin of Nigeria situates on the continental margin of the Gulf of Guinea in the equatorial West Africa between latitudes 3 o and 6 o North and longitudes 5 o and 8 o East.The word "Delta" is derived from a Greek alphabet in shape of a pyramidal triangle.A delta is a geographical feature formed when a River diversifies into numerous streams that sometimes inter-connect into an intricate web of Rivers, lagoons, swamps and wet land.The point where the main rivers divides is the top of the pyramid while the base is where the division ends or the River enters the sea or larger water course such as a lake.The Niger Delta on the Atlantic coast is one of the moist important in the world.Other worlds notable Deltas include the Nile, Mississippi, Orinoco, Ganges and Mekong (Ibru, 2001).Deltas are usually fertile, contain diverse resources and are therefore noted for large human settlements and civilizations.The Niger Delta complex is one of the most prominent basins in West Africa and actually the largest delta in Africa.It includes the Imo River and Cross River deltas and extends into the continental margins of Cameroun and Equatorial Guinea (Reijers et al 1996).
A more rigorous scientific definition of the territory locates it between Aboh to the North, the Benin River to the west and the Imo River to the East.It is located in the Atlantic coast of Southern Nigeria where River Niger divides into numerous tributaries.The area is the second largest delta in the world spanning a coastline of about 450kms foreclosing at Imo River (Awosika, 1995).It is the largest wetland in Africa, spanning over 20,000 square kilometer and among the three (3) largest in the world.It is estimated that about 2,400sq.km of the area consist of rivers, creeks and estuaries while stagnant swamp covers about 8,600sq.km.Its mangrove swamp of 1,900sq.km is the largest in Africa (Awosika, 1995).The area falls within the tropical rain forest zone of Nigeria.The ecosystem is highly diverse and supportive of several species of terrestrial and aquatic flora, fauna and human life.It ranks Fig. 1a.Location map of Niger Delta (Reijers et al, 1996).
amongst the world's most prolific petroleum tertiary delta that together accounts for about 5% of the world's oil and gas reserves and for about 2:55% of the present day basin area on earth.Enormous petroleum reserves in the Niger Delta is estimated at about 30 billion barrels of oil and 260 trillion cubic feet of natural gas ranks the basin 6th in the world production (Reigers et al, 1996).The structural features and petrophysical properties account for the hydrocarbon occurrence.The region is divided into four zones namely coastal inland zone, mangrove swamp zone, fresh water zone and lowland rain forest zone.It has been reported that delta sediments are layered in structure, but layers of alternating sands, silts and clays may not be homogenous (Abam and Okagbue, 1997).Three (3) major formations exist in the area, namely Benin, Agbada and Akata.(Reijers et al 1996).
The Benin formation is mostly continental units of sand mixed with gravel and restricted clays, sequence of sandstone/shale exist in Agbada formation, which is the oil-reservoir in the Niger Delta basin (i.e. oil and gas in the area mainly occur in sandstone reservoirs throughout the Agbada formation).The Akata formation is regarded as over pressured shale (Lambert-Alklionbare et al, 1990).The soil of the area is mostly made up of Entisols and inceptisols, with traces of Alfisols (Ekundayo and Obuekwe, 2001).The dominant fresh water aquifer is found in the Benin formation, though there is shallow aquifer, the thickness of Benin formation generally exceeds 2000m with high consolidation at deep levels (Amadi and Amadi, 1990).Accessible fresh water could occur in the first 100 -200m (Oteze 1983).Water levels can be located at less than 1m near the coast to more than 10m further inland (Amadi, 1986).The whole of delta region receives more than 5000mm of rainfall annually (National Atlas, 1987).Evapo-transpiration is estimated at over 1000mm per year, so there is adequate rainfall to recharge surface and ground water system, although organic matter and clay matrix that consolidate the soil may interfere with infiltration and seapage into the aquifer (Ekundayo and Obuekwe, 2001).The rapid urbanization and industrialization of the Niger delta region of Nigeria occasioned by huge crude oil and gas reserves has had its tole on the environment.Being the most naturally endowed by housing the oil and gas reserves that derive the nation's economy to the vast network of interwoven freshwater aquifers, extensive low lands, tropical and fresh water forest and aquatic ecosystems to its biodiversity with temperature, sunlight and rainfall in an amount and combination that support cultivation and bountiful harvest of rice, sugar cane, yams, plantains, cassava, oil palm, rubber and timber (Nduka et al, 2008).The exploitation of the huge reserve of crude Niger Delta oil and gas deposits has resulted in several million barrels of crude and fractional spillages and several billion cubic feet of gas flaring leading to environmental damage.The US Department of Energy estimates that since 1960, there have been more than four thousand (4,000) oil spills, discharging several million barrels of crude oil into the ponds, ditches, creeks, beaches, streams and rivers of the Niger Delta (Amaize, 2007).

Composition of crude oil
Crude or petroleum based oil refers to a wide range of natural hydrocarbon substances and refined products, each having a different chemical composition.Crude oil is a mixture of highly variable proportion of hydrocarbon but differs from lighter oils to heavier oils and bitumen.It is believed to have been formed several million years ago from decayed remains of animals and plants.Under the effects of heat and pressure, there is breaking down of decayed matter into liquids and gases, both collect into pools under the earth's surface.Definite molecular composition varies widely from formation to formation but the proportion of chemical elements differs little (Speight, 1979).Crude oil is the basic mineral product obtained from the geological strata.Though it is referred to as a single (uniform) mineral substance, in reality crude oil is a complex mixture of thousands of hydrocarbons and non hydrocarbons compounds.Of these, the hydrocarbons (Neumann et al, 1981) are by far the major components linked together with inter atom bonds, these hydrocarbons form a variety of kinds of molecules of many different shapes and sizes.Although crude oil are mixtures of some compounds, but the quantity of individual components vary widely in crude oils from different locations.The physical characteristics of oil, such as density, viscosity, flash point, pour point etc are determined by the characteristics of individual component and their relative quantities within the petroleum specific gravity determines whether a crude oil is classified as light or heavy (Wilson andLeBlanc, 1999/2000).

Other constituents of crude oil
2.1.1Polycyclic aromatic hydrocarbons (PAHs): PAHs is a group of about 100 chemicals that are formed during the incomplete burning of coal, oil, gas, garbage, tobacco and other organic substances.They are also present in crude oil, plastics and pesticides (ATSDR, 1995).

Volatile organic compounds (VOCs):
The most common volatile organic compounds in crude oil are the benzene, toluene, ethylbenzene and xylene.They are also mainly found in household products (paints, paint strippers, solvents, aerosol).

Medium spill
This releases between 25 -250 barrels on inland water or 250 -2500 barrels discharged on land, coastal/offshore water.

Major spill
It releases greater than 250 barrels discharged on inland water or greater than 2,500 barrels discharged on land, coastal/offshore waters.

Fate and behavior of spilled oil
When oil is spilled, over a period it undergoes a number of physical and chemical changes which affect its behavior.These changes start from the spread and drift of the oil through its evaporation, dissolution, dispersion and emulsification to its sedimentation, photooxidation and biodegradation.Biotic factors, like bacteria, yeast and filamentous fungi play an important role in the degradation of petroleum and may be the dominant factor controlling the fate of petroleum hydrocarbons in marine environment (Delaune et al, 1990).

Spreading
The spreading rate of oil will be affected by its viscosity, pour point, wax content, marine state and weather conditions.Slicks formed will move in the same direction and in the same speed as the current and will move in the same direction as the wind at approximately 3% of the wind speed.Less viscous oil spread faster than heavy oils (Clark, 1992), but all oils spread faster on warmer waters.Spreading also induces a change in the composition of the oil by promoting the dissolution and evaporation of certain components, also as hydrocarbon dissolves in water, they alter the water-air interfacial tension (National Research Council, 1985).The force of gravity acting downwards through the thickness of a considerable oil spill tends to spread it out sideways.This movement compares with that of oil on solid surface but limited when the viscosity of the oil counter balances the spreading force.When compared with effect of surface tension, this force becomes operational if there is a difference between the oil/air and oil/water interface tension, while it remains positive, the oil will spread out.Fay (1969), gave a theoretical treatment of the spreading of oils into three (3) separate phases.


Where the spreading rate is controlled by the difference in density between the oil and the water and the speed of spreading controlled by inertia resistance.


Where spreading rate is controlled by gravity but viscous drag between the oil and water limits the spreading rate.


When the spreading is controlled by the surface tension difference between the oil and the water.
Here we consider the third or surface tension type, earlier work on this by Blokker (1964) considered the dynamics of the spreading and proposed an empirical formula based on the assumption that oil spreads in a uniform way where the instantaneous rate of spreading is proportional to the slick thickness.
Blokker's formula thus simplified: An extensive experiment on spreading of oil and its disappearance was carried out by Warren Spring laboratory in 1972 and was described by Jeffrey (1973), here 120 tons of light Arabian crude oil was discharged at sea and its appearance and dimension studied for four (4) days on a uniform water surface, as might be found on the open sea, oil spread evenly in all directions but it is not practicable because of effect of wind and waves.

Evaporation
In evaporation, the rate and extent of evaporation is determined primarily by the volatility of oil, spreading rate, marine and wind conditions and temperature.Evaporation can be responsible for the loss of up to 40% spilled oil in the first day (Jordan and Payne, 1980).The amount of evaporation differs from about 10% in very heavy crude and refined product to as much as 75% in very light crude and refined products (Albers, 1995).From the study of the fate of oil in the Amoco Cadiz spill in 1978, off Brittany, France, it was established that lower molecular weight alkanes and single-ringed aromatics (benzenes) were rapidly depleted through evaporation (Gundlach et al, 1983).

Dissolution
The extent of dissolution is influenced by the oils aqueous solubility which for crude oil is put at 30mg/L (National Research Council, 1985).Low molecular weight aromatics such as benzene, toluene and xylenes which are also among the most volatile has the highest solubility.Actual dissolution of the slick would be expected to account for only around 1% of the mass balance (Mackay and McAuliffe, 1989).

Dispersion
Oil-in-water emulsion or dispersion is due to the incorporation of small globules of oil into the water column.Dispersions are considered beneficial because they increasingly disperse over time and dramatically increase the surface area of the oil available for degradation (Jordan and Payne, 1980).These emulsions are inherently unstable and larger particles tend to rise and coalesce but small droplets can be conveyed with water eddies to become a part of the water column.Oil-in-water dispersions can also be stabilized by suspended particulates (Huang and Elliot, 1987).

Emulsification
Low viscosity oils tend to form emulsion very quickly (2 to 3 hours) and can be up to 80% content.Oils that have asphaltenes content, 70.5% are likely to form stable emulsion.These emulsions are problematic because they slow microbial degradation and are resistant to dispersion (Payne and Philips, 1985).

Sedimentation
Sedimentation of oil is facilitated by the sorption of hydrocarbons to particulate matter suspended in the water column.Since coastal environment of the Niger Delta contains large amount of suspended particulate matter (Nduka and Orisakwe, 2011), adsorption of oil onto suspended particulate matter results in a high specific gravity mixture more than twice that of sea water alone (1.025g/cm 3 ).The high specific gravity of these particles causes deposition of the sorbed oil (Kennish, 1997).Increasing density of oil due to weathering can also promote its movement below the surface into the water column and eventually into sediments (National Research Council, 1985).

Photo-oxidation
UV radiation has enough energy to transform many petroleum hydrocarbons into compounds possessing significant chemical and biological activity (Jordan and Payne, 1980).
The mechanism is known as auto catalytic free-radical chain reaction, which results in the formation of hydroxyl compounds, aldehydes, ketones and low molecular weight carboxylic acids (Burrwood andSpeers, 1974, Jordan andPayne, 1980).Photo-oxidation of hydrocarbons derived from crude oil can occur from evaporated components in the gaseous state (Baek et al, 1991), from the dissolved fraction of petroleum (Neff, 1985) and from non dissolved oil like slicks and colloidally dispersed oil (Jordan an Payne, 1980).Organosulphur compounds reduce complete oxidation to carboxylic acids by leading to termination of free radical chain reaction (Jordan and Payne, 1980).Photo-oxidation rates can be increased by the presence of photo-sensitizing compounds such as xanthone-1-naphthol and other naphthalene derivatives and by the effect of dissolved ions of variable oxidation state such as vanadium that acts as catalysts (Jordan and Payne, 1980).Obviously, throughout the life of an oil slick, it continues to drift on the sea surface.The wind induced effect is normally taken as 3% of the wind velocity and the current effect is taken as 100% of the current velocity.

Time scale for different process in weathering
Scheme 1.

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Crude Oil Exploration in the World 56

Micro-bial degradation
Micro-organism indigenous to soil, groundwater and marine ecosystems degrade a wide range of compounds like aromatic and aliphatic hydrocarbons, chlorinated solvents and pesticides released into natural environment (BICNEWS, 2005).Since empirical evidence that aromatic hydrocarbons exist in the Niger Delta marine ecosystem due to extensive crude oil and gas exploitation, fire explosions, leachlets from decomposing refuse and industrial effluents (Okoro and Ikolo, 2005;Anyakora et al 2004;Anyakora and Coker 2006;Olajire et al, 2005), native microbes could be assisting Nigerians in the Niger Delta region in cleaning water system unnoticeable and free of charge.From our work (Nduka and Orisakwe, 2011), fewer or no counts of achromobacter and aspergillus (polyaromatic hydrocarbon (PAHs) degraders) and proteus (straight chain hydrocarbon degraders) were found in most water samples while bacillus and pseudomonas, both PAHs and straight chain hydrocarbon degraders (Rosenberg, 1993), were found in highest counts and in almost all the water samples.It was evident that water samples in which PAHs and straight chain hydrocarbon were highest, had highest microbial count per specie (figs 2a, 2b, 2c and Tables 2 and 3) (Nduka and Orisakwe, 2011).Therefore the low levels or non detection of PAHs and straight chain hydrocarbons could mean degradation by microbes (utilization of carbon as food by microbes for sustenance).This observation agrees with previous report (Atlas 1991, Young andCerninglia 1995).Heavy and complex compounds are more resistant to microbial degradation, but many are degradable by micro organism to a large extent.Some of the heavy and more complex compounds will eventually settle to the marine floor (Neilson, 1994).Put together, 40 to 80% of crude oil can be degraded due to microbial action (Albers, 1995).The most significant factors that affect crude oil (hydrocarbon) degradation by microbes include microbe type, water temperature, nutrient availability, amount of oxygen, salinity and bioavaible surface of the oil (Atlas andBartha, 1973, Kennish, 1997).Microbial degradation is inhibited by mouse formation (which reduces the surface area of the oil available to biodegradation) and by cool water temperatures (Galt et al, 1991).Anaerobic conditions severely restrict microbial degradation (Gundlach et al, 1983).Oil deposited in the bottom sediments of sheltered estuaries and wetlands can persist for more than ten(10) years (Teal, 1993).

Crude oil toxicity
Toxicity of crude oil largely depends on the concentration of oil in water, dispersed into the water at low concentration (<1ppm), it is very little problem and will quickly get broken down.At higher concentration, it is toxic to most life forms and floating on the surface of water, it will physically smoother on everything it touches.The majority of most types of oil will float on water surface when spilled, but some will dissolve into water and with the help of wave action, some will be dispersed into small droplets.The most likely impact of oil floating in the sea is on the sea birds.Any oil sinking down into the water, both dissolved and dispersed could affect marine life particularly if the water is shallow and the oil toxic.
It is unusual, however for significant concentration of oil to go deeper than 5 metres below the surface, so there is not usually great concern for marine life below this depth.(SPDC, Nigeria, 1997).

Planktons
Planktons are the basis of marine food chain and it includes eggs and larvae of fish and other animals.It is very sensitive to the toxicity of oil and lots of planktonic organism will be killed, particularly if the concentration of oil in the water is increased by the wave action or chemical dispersants, therefore it is possible in a worst case scenario for the effect on the plankton to lead to some longer term effect ( Adeyemi, 2004).

Aqua culture
Fish in fish farms are trapped by the nets and cannot escape the oil while it is quite likely that the fish may not die since they are tolerant to oil; they will be likely tainted.Tainting is where the fish absorbs oil from the water and its flesh when eaten tastes off, if the tainting is severe which is most likely to happen if a lot of oil has been dispersed into the water, the fish may be indelible leading to economic loss (SPDC Nigeria 1997, Adeyemi, 2004).

Fish
Adult fish have very sensitive sense organs so they taste the oil and quickly leave the area of the spill, unless they are trapped there in some way.It is very rare to have large fish kills due to marine oil spills.Juvenile fish however are more vulnerable since they often live in shallow water near shore areas known as "nursery areas" until they become adult.If a toxic oil impact a shallow bay and the oil is dispersed down into the water, the increased concentrations could have severe effects on juveniles and will result in long term impacts on adult fish stocks.This been evidenced in the Niger-delta region of Nigeria.Polyaromatic hydrocarbon (a carcinogen), been lipophylic tend to accumulate more in fish than in the sediment and least in the water samples of the region.Fish therefore is the best biomarker for the levels of PAHs contamination in marine samples (Anyakora et al, 2005).Nitrate pollution which has been reported in the area (Nduka and Orisakwe, 2011), at increased concentrations are harmful to aquatic animals.Marine invertebrates and fish exposed to nitrate may be smaller in size, have reduced maturity rate and lower reproductive success.
In extreme high exposure levels, aquatic invertebrates and fish may die (Ohio State University, 2008).Early life stages of aquatic animals are more sensitive to nitrate than juvenile and adult animals.Early studies by Gbadebo et al, 2009, showed that petroleum oil, whether crude oil or spent oil is very toxic to fish (Clarias garipinus fingerlings), but spent oil produced more toxic effects on the clarias fingerlings at every concentration than that of crude oil.Their findings is supported by the fact that the water-soluble components of crude oil are toxic and could affect the survival and metabolism of aquatic animals like fish (Cote, 1976).

Sea birds
Sea birds are very easily affected by oil on the surface water because they spend long period sitting on the water.The oil is soaked up by their feathers and cannot fly, feed or preen themselves.They ingest oil which then damages their gut, die of starvation, cold, poisoning or shock.The sensitivity of species of birds to presence of oil vary.The impact on local population of birds can be serious and result in reduced population for many years (SPDC, Nigeria, 1997).In their work, Fry et al, 1986, showed that when wedge-tailed shearwaters birds were exposed to weathered Santa Barbara crude oil, it resulted in a greatly reduced number of eggs laid and complete hatching failure of 60 pair of exposed birds.Oral doses of oil in gelatin capsules reduced laying and breeding success but to a lesser extent than external exposure, also survival of chicks of dosed birds were reduced.It has also been observed that exposure of birds to crude oil before breeding delayed sexual maturation or onset of lay of eggs in captive mallards (Holmes et al, 1978, Coon andDieter, 1981).Some crude oils are embryotoxic and if ingested during the period of egg formation may affect the development of progeny (Gorsline and Holmes, 1982b).

Dispersant problem
To stem the effect of oil spill, different grade of chemicals (dispersants) were developed to dispose the oil and subsequently hasten its sinking.The use of dispersants to deal with oil spills should be seen as an aid to the process of natural dispersion.Dispersants reduce surface tension of oil/water interface thereby breaking the oil slick into fine droplets that are then dispersed into the water column, for each dispersant, there will be a different range of effectiveness.The range of effectiveness is related to the concentration of the emulsifiers in the formulation, the effectiveness of the emulsifiers and the type of solvent used.
One of the disadvantages of dispersants is that they introduce a second source of pollution into the marine environment and indeed most of the opposition to their use stems from this fact.If a dispersant works effectively, then it is removing the oil from the water surface and distributing it throughout the body of the water.The upper section (normally top 3 metres) of the water column will contain fairly high concentrations of oil and this may reach toxic levels (SPDC, Nigeria 1997).

Chemical pollution associated with oil spill
Apart from environmental devastation associated with oil spill, the chemical constituents of the spilled oil induce toxic effect to the plant, animals, man and aquatic organism.Polyaromatic hydrocarbon (PAHs) are a class of compounds composed of two or more aromatic rings.They are a component of crude and refined petroleum products.Petroleum production, import and export of petroleum products also contribute a lot to the extent of PAH contamination especially in the marine samples (Baek et al 1991, Lorber et al 1994, Nwachukwu 2000, Nwachukwu et al 2001).They have been reported in water samples, fish species and soil sediments of the Niger Delta region of Nigeria which has had extensive petroleum production activities over the past few decades (Anyakora et al 2005, Anyakora and Coker 2006, Anyakora et al 2005).PAHs are classified as environmentally hazardous organic compounds due to their known or suspected carcinogenicity and are included in the European community (EC) and United States Environmental Protection Agency (USEPA) priority pollutant list (Nieva-Cano et al, 2001).These, with metals, volatile organic compounds (VOCs), and others have been previously discussed under composition of crude oil.

Air pollution resulting from crude oil refining and gas flaring
Crude oil exploration in the Niger delta region Nigeria has resulted in gas flaring, fire and gas explosions and bush burning, results in air borne particulate matter, also called suspended particulate matter (SPM) can be found in ambient air in the form of dust, smoke or other aerosols.SPM can occur as a secondary aerosol resulting from atmospheric transformation of gaseous pollutants emitted from combustion sources such as power plants and automobiles or natural sources such as forests.Particles can also result from condensation of volatile elements and species in the atmosphere and form very small particles or absorbed on the surface of already formed, finely divided particles.The combustion of crude oil associated gas (flaring) releases several gases into the atmosphere.Carbon monoxide (CO) is emitted into the atmosphere mainly as a product of the gas, it is accompanied by release of carbon (iv) 2 ) (a green house gas) (Ideriah and Stanley, 2008).Average value of 69.25 µgm -3 of CO z level have been reported in Niger-delta.Release of CO 2 has potential to adversely affect the health and well-being of nearby organisms (Nwaichi and Uzazobona 2011).Hydrogen sulphide is also present in air as a result of gas flaring, although Nigerian crude oil is reputed to have few milligram per litre of sulphur.H 2 S can also result from microbial decay of organic matter and sulphate ion reduction Sea water as found in the Niger delta region has high sulphate ion, bacterially induced formation of H 2 S causes pollution problems in coastal regions as in our study area and is a major source of atmospheric sulphur (Manahan, 1979).Oxides of nitrogen (N0 x ) and ammonia can also result from crude oil associated gas flaring and refining operations Ammonia in polluted atmosphere reacts readily with acidic materials.Such as sulphuric acid aerosol droplets to form ammonium salts (Ideriah and Stanley, 2008).
Oxides of sulphur (SO x ) and that of nitrogen (NO x ) primarily affect the respiratory system and studies on laboratory animals and humans show that these pollutants irritate the lining of the lungs and cause respiratory stress (Coffin and Stokinger, 1976).Organisms are exposed to air pollutants enroute three pathways: (1) Inhalation of gases or small particles, (2) Ingestion of particles suspended in food or water and (3) absorption of gases through the skin.Organisms response to pollutants varies and depends on the type of pollutants involved, exposure time and volume of pollutants taken up by the animal.Organism's age, sex, health and reproductive condition also play a role in its response (Maniero, 1996).The most outstanding effect of air pollution resulting from flaring of crude oil associated gas and petroleum refining activities in the Niger-delta region of Nigeria is acid rain.Over 2.5 billion Fe 3 of crude-associated gas is flared in Nigeria daily with an estimated yearly financial loss of $2.5billion.Acid rain pre-cursor gases -NO 2 and SO 2 are products of high temperature reactions and gas flaring in the study, area makes this possible, hence we have reported acid rain in our previous studies (Nduka et al 2008, Nduka andOrisakwe 2010).Acid precipitation can wear away the waxy protective coatings of leaves, damage them and reduce photosynthesis.Important cations such as K + , Ca 2+ , mg 2+ and Na + , which are very important to the welfare of green plants and the aquatic ecosystem, are leached out and become unavailable to plants, also toxic cations such as Pb 2+ , Cd 2+ , Hg 2+ are demobilized into the aquatic ecosystem where they bioconcentrate in lugworms, barnacles, algae and other planktonic and benthic organisms enroute to food webs.Sulphates and nitrates, which form in the atmosphere from sulphur dioxide (SO 2 ) and nitrogen oxide (N0 2 ) emissions, contribute to visibility impairment.The ubiquitous soot (black carbon) or Charcoal (Goldberg, 1985) which normally give rise to black rain in Niger-delta region of Nigeria is one of the major components of air pollution worldwide.

Public health impact resulting from crude oil exploration and exploitation
Apart from acidic precipitation and its negative impact, acid rain precursor gases (N0 2 and SO 2 ) are part of six (6) common outdoor pollutants (ALA, 1996).Noise and thermal pollution from numerous gas flare points and extensive fire disasters that characterize the study area have led to extinction of some exotic species that are hunters delight.Inhalation of fine particulates that are fallouts from acid precursor gases have been linked to illness and premature death from heart and lung disorders such as asthma and bronchitis (USEPA, 2001).Nitrogen dioxide (NO 2 ) poses a health threat itself as well as playing a major role in the formation of the photochemical pollutant ozone.Previous studies has shown that animals exposed to NO 2 have diminished resistance to both bacterial and viral infection (Gardner, 1984), while children exposed to high indoor levels of NO 2 may become more susceptible to critical infections of the lower respiratory tract, bronchial tubes and lungs, and may develop bronchitis and chest cough with phlegm (Neas et al, 1991).Sulphur dioxide (SO 2 ) is a temporary irritant, though research have shown that increased levels of SO 2 in conjunction with particulate matter may trigger small, but measurable, temporary deficits in lung function (Dockery et al, 1986).Epidemiological studies have found that the impact of SO 2 is inseparable from that of particulate matter, but effects of the two classes of pollutants have been differentiated by an analysis exemplified by studies in Uta valley (Pope et al, 1992).The major health impact of SO 2 is on population groups susceptible to pollutant effect due to pre-existing conditions, such as asthma.Measurable atmospheric levels of SO 2 and NO 2 exist in the Niger-delta region of Nigeria which gave rise to acidic precipitation we have reported in the region (Nduka and Orisakwe, 2010).In the area, serious health problems such as skin cancers and lesions may be linked to acid rain.Stomach ulcers could also occur, as consumption of acidic water can alter the pH of the stomach and leach the mucous membrane of the intestinal walls, this is more so as Nigerians depends heavily on rain water for drinking, cooking, laundry and other domestic uses.
Degradation processes such as photolysis, hydrolysis, oxidation and biodegradation are all involved in the chemical transformation of a compound upon its entry into the environment.The value of C 10 to C 3 o straight chain hydrocarbon and the concentrations of chloride ion in the water samples of the Niger Delta region of Nigeria, shows that the formation of polychlorinated-n-alkanes (PCAs) of the general formular C n H 2n + 2 -Z cl 2 is possible (Nduka and Orisakwe, 2011).Polychlorinated-n-alkanes (PCAs) are normally manufactured in the presence of ultra violet (UV) light (Tony et al. 1998).The surface water of the region where crude oil spill occurs are wide open to direct ultra violet (UV) light from the sun, its formation is by simple substitution of hydrogen atoms by chlorine atoms, an example of chain reaction involving free radicals (Morrison and Boyo, 1983), also for the fact that the temperatures of water are above ambient values even in rainy season (Nduka and Orisakwe, 2011) shows that their formation is possible.Those of great interest are the C 10 -C 13 PCAs, which have the greatest potential for environmental release (Environmental Canada 1993a) and the highest toxicity of PCA products (Serrone et al, 1987, Wills et al 1994, Mukherjee, 1990).Taken together, the carcinogenic effect of Polyaromatic hydrocarbons (PAHs) and the fact that study has shown that the C 10 -C 13 PCAs inhibit intercellular communication in rat liver epithelial cells, a phenomenon that suggests these chemical may be acting as tumor promoters (Kato, 1996), could accelerate environmental and public health hazards such as malignant lymphomas (Omoti andHalim 2005, Omoti, 2006) and soft tissues sarcomas (Seleye-fubara et al, 2005) already reported in the Niger Delta region of Nigeria.In addition to these above, high nitrate levels in water samples from the region can also result in incidences of some cancers and lesions (Gulis et al, 2002), spontaneous abortion and ectopic pregnancy also reported in the area (Gbaforo and Igbafe, 2002).Pollution keratoconjuctivitis have been reported among children in oil-producing areas of Niger Delta, Nigeria.It has adverse consequences due to accumulation of differed categories of pollutants from drilling, production, refining of crude oil and production of petrochemicals, mainly black carbon.Persistent itching, foreign body sensation and specified areas of conjunctiva/limbal discoloration were used as markers for Pollution Kerato Conjunctivitis (PKC) (Asonye and Bellow, 2004).In their work investigation into the pharmacological basis for some of the folkloric uses of bonny light crude oil in Nigeria, Orisakwe et al, 2000, discovered that Nigerian bonny light crude oil caused complete inhibition of histamine-induced smooth muscle contraction while producing only a partial inhibition of the acetylcholine-induced contraction.It had no effects on the acetylcholineinduced skeletal muscle contraction, but proved good to analgesic effect that is comparable to aspirin.Because of complex composition of crude oil, it has multiple potential type of toxic effect which may include long term petroleum pollution on individual organism such as impaired reproduction (Feuston et al, 1997), reduced growth (Eisler, 1987), tumours and lesions (Malins and Ostrander, 1994), blood disorders (Yamato et al 1996) and morphological abnormalities (Kennish, 1997).Crude oil showed changes in the hypothalamo-pituitary-thyroid adrenal axis when male rats were exposed to it, and the effect is believed to be due to stress (Vyskocil et al, 1988).The Nigeria nation has an outrageous twelve million infertile people though not restricted to oil producing areas alone (Giwa-Osagie, 2003, whose infertility is believed to be due to infection (Cates et al, 1985), although some infection do persist after treatment.There are elevated consistence oligospermia or azoospermia in Nigeria than most other causes of infertility and less resources for its management (Osegbe and Amaku, 1985).Therefore it has been established that the Nigerian bonny light crude oil is a testicular toxicant and its use as a folklore medicine (which is very ubiquitous) in Nigeria may cause infertility (Orisakwe et al, 2004).
They have also reported that the kidney cells of an adult albino rats were damaged by bonny light crude; crude oil caused a destruction of the renal reserve capacity (Orisakwe et al 2004).

Conclusion
Commercial exploration and exploitation of huge crude oil deposits and gas reserves in the Niger-Delta region of Nigeria has resulted in the alteration of the regions environment in certain negative manner.Vegetation is cleared to make way for seismic lines, roads are built, drilling mud and oil may reach surface water.The effect is the millions of barrels of crude oil and its lower fraction spills that results from various operations, damaging valuable commodities in the environment, plants and animals, harbours, beaches, marinas are devastated making them unfit for use.Due to its complicated composition, petroleum hydrocarbon has the potential to eliciting various toxic effects, which can cause acute lethal toxicity, sub lethal chronic toxicity or both depending on the exposure, dosage and type of organism exposed.Toxicity is not restricted to the immediate surrounding of the spill due to

Fig. 2a .
Fig. 2a.Some PAHs (mg/l) in water sample from Anieze river in River State.

Fig. 2b .
Fig. 2b.Some PAHs (mg/l) in water sample from Orashi River in Rivers State.

Table 3 .
(Nduka and Orisakwe, 2011)pillages Resulting from Exploration and Exploitation in Niger-Delta Region of Nigeria: A Review About the Environmental and Public Health Impact 59 Amount (Mg/L) Of Bacterial Count In Selected Water Samples Of Niger Delta(Nduka and Orisakwe, 2011)Impact of Crude Oil Spill on the water organism. www.intechopen.com